The resistance of positive temperature coefficient (PTC) conductive composite materials maintains extremely low under normal temperature, and can react to temperature changes very quickly. When an overcurrent or an over-temperature occurs, these materials exhibit a sharp increase in resistivity which leads to open circuit and the protection of the circuit or the device. Therefore, this kind of conductive composite materials has been widely used as circuit protection component.
The PTC conductive composite materials usually include a matrix of crystalline polymer material in which conductive fillers are uniformly dispersed on the macroscopic. The polymers are polyolefin and their copolymers generally, such as polyethylene and ethylene-vinyl acetate copolymer. Meanwhile, the conductive filler is generally carbon black, metal powder or conductive ceramic powder. As the special aggregate structure of carbon black and polar group on its surface, the carbon black and polymer adhere well. So that the PTC materials, with carbon black as conductive filler, have good resistance stability. However, because of the limited conductive capacity of carbon black, it can't satisfy the need of low resistance. At the same time, the PTC materials, with mental power as conductive filler, have extremely resistance. But it needs encapsulation of conductive composite materials to prevent oxidation of the metal powder in the air, which can lead to the increasing of resistance. Whereas, the volume of overcurrent protection devices can't be reduced effectively after encapsulated, which is difficult to meet the requirements of miniaturization of electronic components. To obtain low resistance and meet the requirements of miniaturization of electronic components, it tends to use the metal carbide ceramic powder (such as titanium carbide) as conductive filler of PTC conductive composite materials. But as poor combination of metal carbide ceramic powder and polymer, the reproducibility of resistance is difficult to control for this kind of conductive materials.